Geobg buhier



Dec. 17, 1929. 4 G BUHLER' 1,739,542

CORE FOR MOLDS Filed Oct. 29, 1928 Patented Dec. 17, 1929 PATENT, OFFICE GEORG BlZl'HLER, F VIENNA, AUSTRIA oonn FOR MOLDS Application filed October 29, 1928, Serial No.

This invention relatesto resilient cores for molds used for casting diflerentmetals especially for the production of draw holes or the like for the production of tubes of pure bronze. i The manufacture of bronze tubes offers difficulties, and it is only possible to produce the desired final shape by drawing the holes obtained by casting when they are quite faultless and without the smallest irregularity in structure. It has been scarcely possible by previous methods to obtain bronze draw-holes suitable for further drawing, and the impossibility of obtaining'such bronze tubes of the desired dimensions by the usual drawing processes has hitherto been generally attributed to the fact that the material is too brittle. I

It has now been found, that really faultless bronze draw-holes could be worked by drawing to a very large extent. However, in order that a useful rough casting for further treatment'may be obtained, 'it is necessary that after casting the bronze shall be capable of freely moving in the mold during cooling. It is known, that on the cooling of mixtures of metals in the liquid state within solid and rigid receptacles, especially when solid cores are used, fine hair-cracks are very easily formed in the walls of the hollow casting, which on further drawing of the casting produce defective and therefore useless tubes. I have now ascertained that the formation of defective hollow castings can be avoided, by inserting a resilient core in the chill molds, which gives way without resistance to the motion of the metal during cooling and so pre- 'vents the production of undesired strains in the metal.

Such resilient cores have hitherto been unknown. Their production offers great difficulties since it is diflicult to combine the requirement of suflicient rigidity during the casting process with the necessary give or elasticity. I have succeeded in solving this problem by making the core in a particular way, of sand and sawdust and by providing it with an envelope of clay and graphite. Usually two parts of the ordinary, somewhat clayey, molding sand are used with one part 315,817, and in Germany November 4, 1927.

ofsawdust. The sawdust is soaked in water until it has reached its maximum volume. Then by pressing in a small press (an ordinary fruit press suffices for this purpose) the greater part of the water is removed. The I sand and sawdust must be mixed together as intimately as possible. This is ensured by passing the mixture at least three times through a fine sieve. The uniform mixture of sand and sawdust so obtained is then filled into the core casing. The latter which consists of two parts held together by precision. pins and wedges, is set upright and the core rod which is provided with a centring disc is introduced therein. In order to facilitate the filling in of the material a small metal funnel may be placed at the top. Before the mixture of sawdust, and sand is introduced, a layer of pure sand is put in and stamped down'as hard as possible with an iron rod. The casing is then filled with the mixture of sawdust and sand nearly up to the top, the mixture being only loosely stamped in by means of a wooden stick. Thereupon, more pure ,sand is introduced, which must be stamped down hard. The mixture of sand and sawdust is thus provided at the upper and lower extremities, with a hard ring of pure sand. The lower hard ring is intended for the subsequent insertion of the core into the lower part of the chill mold and the upper hard ring for the insertion into the centring ring of the mold. These parts must have sufficient rigidity so as not to collapse during the insertion. s5 After the core has been stamped down, the core-receptacle is opened and the core lifted out. When freshly stamped it is very fragile and therefore it must be handled very carefully in order that it shall not fall from the core-rod. In order to render further working possible the core is allowed to dry in the air for 24 hours. The solidity of the core is thereby so very much increased that it can be further treated. This further treatment consists in this that the core is rapidly dipped into a thick liquid mixture of clay and graphite. By this means the surfaceof the core absorbs so much of this thick liquid mixture, that a continuous skin is formed upon it.

The core provided with this skin is then introduced into the drying chamber. A temperature of 80 C. is produced in this drying chamber when the cores are suspended in it. At this temperature the cores dry very rapidly and obtain a hard surface. When this state is attained, the furnace isheated up until the whole of the drying chamber becomes incandescent. The cores hanging within also become incandescent and the wood material they contain is burnt, so that'the substanceof the cores is provided with numerous pores.

The burned core has, so to speak, a kind of and Fig. 3 a plan view of Fig.2.

The core case, usually made of castiron consists of two parts 1 and 2, whichcarry the conical precision pins 3 and which are held together by the pressurewedges d. The core rod 5 is placed centrally in the mold. At-the lower end of the'inold there is providedan annular member 6, composed of two parts preferably made of steel. In orderto pro duce the core, first enough pure sand is intro duced to fill the same member 6- and a small part of the mold above. As already mentioned, this sand is stamped down as hard as possible, so that the lower portion 7 of the prepared core has sufficient rigidity to be mserted into the lower piece of the chillmold. The uniform mixture of sawdustand sand, which forms the main part ofthe core 8, is then introduced. This mass is only loosely stamped down. On top of this comes another layer of pure sand, stamped down as solid as possible, which constitutes the upperpart 9 of the core. After the core has been completely stamped down, a duct 10, to carry away the gases evolved during the burning, is pierced, usually near the core rod 5, by means of a rod of suitable thickness. After the core has been removed from the mold and air- Fig. 2 a sectional elevation of the core case,

to ensure that the desired internal diameter of the casting will be obtained.

What I claim is 1. A resilient core for casting-molds made of a burnt mixture of sand and sawdust and having an outer covering of graphite and clay.

2A process for the production of a resilient core for casting molds consisting in introducing into acore mold having a core rod,"iirst alay'er'of sand which is stamped down solid, then a mixture of sand and water soaked sawdust which is lightly stamped down, and finally; a further layer of sand which is stamped down solid, then piercing an air passage nearly to thebottom of the core by the introduction of a thin rod, removiii-g the corefi'om the mold and 'dipping it into athicld aqueous fluid mixture of clay and graphite, drying in a chamber at (50 to 8!) C. and thenraisingthe' temperature of the core and chamber to incandescence.

In: testimonywhereof I have signed my name to this specification;

enoae BUHLER;

IOU

lUfi 

